Segment registry into public and private components

[alnoki]

Presently, the Econia registry is not publicly exposed so as to prevent excessive public queries, and thus transaction collisions against the registry that may result when new markets are registered.

To enable ease of market info lookup, it is proposed that the registry be separated into public and private portions:
here, the public element could be a table without length, such that once a new market is registered it can be looked up via read-only operations as needed. The private element could track number of issued capabilities, markets, etc. and could be updated only when registrants pay for operations with utility coins.